the human population

future population growth

The growth of the human population has started to slow down. You can see this in Figure 18.21. It may stop growing by the mid 2000s. Scientists think that the human population will peak at about 9 billion people. What will need to change for the population to stop growing then?

recent population growth

More recently, the death rate has fallen because of the availability of more food and medical advances: A green revolution began in the mid 1900s. New methods and products increased how much food could be grown. For example, chemicals were developed that killed weeds without harming crops. Pesticides were developed that killed pests that destroyed crops. Vaccinations were developed that could prevent many diseases (see Figure 18.19). Antibiotics were discov- ered that could cure most infections caused by bacteria. Together, these two advances saved countless lives. Today in many countries, death rates have gone down but birth rates remain high. This means that the population is growing. Figure 18.20 shows the growth rates of human populations all over the world.

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sustainable development

Is it possible for all the worlds people to live well and still protect the planet? Thats the aim of sustainable development. Its goals are to: 1. Distribute resources fairly. 2. Conserve resources so they wont run out. 3. Use resources in ways that wont harm ecosystems. A smaller human population may be part of the solution. Better use of resources is another part. For example, when forests are logged, new trees should be planted. Everyone can help in the effort. What will you do?

human population and the environment

Are 9 billion people the human carrying capacity? It looks that way in Figure 18.21. But some people think there are too many of us already. Thats because we are harming the environment. Supplying all those people with energy creates a lot of pollution. For example, huge oil spills have killed millions of living things. Burning fossil fuels pollutes the air. This also increases causes global warming. Fossil fuels and other resources are being used up. We may run out of oil by the mid 2000s. Many other resources will run out sooner or later. People are killing too many animals for food. For example, some of the best fishing grounds in the oceans have almost no fish left. People have destroyed many habitats. For example, theyve drained millions of acres of wetlands. Wetlands have a great diversity of species. As wetlands shrink, species go extinct. People have allowed alien or invasive species - species originally from a different area - to invade new habitats. Often, the aliens have no natural enemies in their new home. They may drive native species extinct. Figure People themselves are also affected by the large size of the human population. A minority of people use most of the worlds energy and other resources. Many other people lack resources. Many dont have enough to eat or live with

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population growth rate

The population growth rate is how fast a population is growing. The letter r stands for the growth rate. The growth rate equals the number of new members added to the population in a year for each 100 members already in the population. The growth rate includes new members added to the population and old members removed from the population. Births add new members to the population. Deaths remove members from the population. The formula for population growth rate is: r = b - d, where b = birth rate (number of births in 1 year per 100 population members) d = death rate (number of deaths in 1 year per 100 population members) If the birth rate is greater than the death rate, r is positive. This means that the population is growing bigger. For example, if b = 10 and d = 8, r = 2. This means that the population is growing by 2 individuals per year for every 100 members of the population. This may not sound like much, but its a fairly high rate of growth. A population growing at this rate would double in size in just 35 years! If the birth rate is less than the death rate, r is negative. This means that the population is becoming smaller. What do you think might cause this to happen?

carrying capacity

A population cant keep growing bigger and bigger forever. Sooner or later, it will run out of things it needs. For a given species, there is a maximum population that can be supported by the environment. This maximum is called the carrying capacity. When a population gets close to the carrying capacity, it usually grows more slowly. You can see this in Figure 18.16. When the population reaches the carrying capacity, it stops growing.

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how populations grow

A population usually grows when it has what it needs. If theres plenty of food and other resources, the population will get bigger. Look at Table 18.1. It shows how a population of bacteria grew. A single bacteria cell was added to a container of nutrients. Conditions were ideal. The bacteria divided every 30 minutes. After just 10 hours, there were more than a million bacteria! Assume the bacteria population keeps growing at this rate. How many bacteria will there be at 10.5 hours? Or at 12 hours? Time (hours) 0 0.5 Number of Bacteria 1 2 Time (hours) 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10 Number of Bacteria 4 8 16 32 64 128 256 512 1,024 2,048 4,096 8,192 16,384 32,768 65,536 131,072 262,144 524,288 1,048,576

human population growth

Figure 18.17 shows how the human population has grown. It grew very slowly for tens of thousands of years. Then, in the 1800s, something happened to change all that. The human population started to grow much faster.

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the demographic transition

The industrial revolution is what happened. The industrial revolution began in the late 1700s in Europe, North America, and a few other places. In these places, the human population grew faster. While there had always been a lot of births, the population grew because the death rate fell. It fell for several reasons: 1. New farm machines were invented. They increased the amount of food that could be produced. With more food, people were healthier and could live longer. 2. Steam engines and railroads were built. These machines could quickly carry food long distances. This made food shortages less likely. 3. Sanitation was improved. Sewers were dug to carry away human wastes (see Figure 18.18). This helped reduce the spread of disease. With better food and less chance of disease, the death rate fell. More children lived long enough to reach adulthood and have children of their own. As the death rate fell, the birth rate stayed high for a while. This caused rapid population growth. However, the birth rate in these countries has since fallen to a rate close to that of the low death rate. The result was slow population growth once again. These changes are called the demographic transition.

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instructional diagrams

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questions

The population growth rate equals the number of births in a year per 100 people.

a. true

-->  b. false

If the birth rate is less than the death rate, then the population has a growth rate of zero.

a. true

-->  b. false

There is no limit on how large a population can grow.

a. true

-->  b. false

The human population started to grow rapidly in the 1800s.

-->  a. true

b. false

In the first phase of the demographic transition, populations grew slowly.

a. true

-->  b. false

Pesticides increase crop production by killing weed plants.

a. true

-->  b. false

Human population growth rates are highest in the United States.

a. true

-->  b. false

We may run out of oil by the mid-2000s.

-->  a. true

b. false

Alien species can cause native species to go extinct.

-->  a. true

b. false

Some people think that sustainable development may require a smaller human population.

-->  a. true

b. false

annual births minus deaths per 100 population members

a. green revolution

b. vaccine

c. carrying capacity

-->  d. population growth rate

e. demographic transition

f. antibiotic

g. sustainable development

drug that kills bacteria

a. green revolution

b. vaccine

c. carrying capacity

d. population growth rate

e. demographic transition

-->  f. antibiotic

g. sustainable development

using resources in a way that gives everyone enough and protects the environment

a. green revolution

b. vaccine

c. carrying capacity

d. population growth rate

e. demographic transition

f. antibiotic

-->  g. sustainable development

substance that prevents a disease

a. green revolution

-->  b. vaccine

c. carrying capacity

d. population growth rate

e. demographic transition

f. antibiotic

g. sustainable development

largest population that can be supported by the environment

a. green revolution

b. vaccine

-->  c. carrying capacity

d. population growth rate

e. demographic transition

f. antibiotic

g. sustainable development

change from high birth and death rates to low birth and death rates

a. green revolution

b. vaccine

c. carrying capacity

d. population growth rate

-->  e. demographic transition

f. antibiotic

g. sustainable development

increase in food production due to new products and methods

-->  a. green revolution

b. vaccine

c. carrying capacity

d. population growth rate

e. demographic transition

f. antibiotic

g. sustainable development

About how many people live on Earth?

a. 7 million

-->  b. 7 billion

c. 9 billion

d. 7 trillion

If the birth rate is greater than the death rate, then

a. d is negative.

b. b is negative.

-->  c. r is positive.

d. two of the above

If a population reaches its carrying capacity, it is most likely to

a. grow rapidly.

-->  b. stop growing.

c. increase its size.

d. increase its carrying capacity.

Food production increased during the

a. green revolution.

b. demographic transition.

c. industrial revolution.

-->  d. all of the above

Human actions that lower death rates include

a. improving sanitation.

b. vaccinating children.

c. purifying water.

-->  d. all of the above

Some people think that the human population has reached its carrying capacity because

a. we are saving the environment.

b. everyone has just enough resources.

c. we have enough fossil fuels for decades.

-->  d. none of the above

Goals of sustainable development include

a. conserving resources.

b. distributing resources fairly.

c. using resources in ways that do not harm ecosystems.

-->  d. all of the above

diagram questions

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